Begin with an attention grabber that sets the theme for your personal statement and relates to why you chose the particular field of medicine you studied in school. Quotes, anecdotes, or touching stories make for good attention grabbers.
Transition from the attention grabber to a discussion about how you became interested in the field you chose. Use concrete examples to show the residency committee what the spark or catalyst was that made you want to pursue a career in that specific medical field.
Explain what you are looking for in a residency program in your second paragraph. Bridge the first and second paragraph by discussing what impresses you about the specific residency program you are applying for and how that residency program meets your needs.
Conclude your personal statement for residency by discussing your goals. Talk about what impact you want to have on the field you chose and explain how you believe a residency at the chosen facility would help you accomplish those goals.
Bring your draft to a writing center (such as your medical school's writing office, if it has one) and have someone proofread the document. Rewrite the essay and try to weave in your theme and your anecdotes throughout the essay to give it a cohesive feel and to make it interesting to read.